As the need for increased data storage changes, the search for higher density, faster access memory technologies also increases. One of these, holographic data storage, provides the promise for increased access to higher density data. The techniques for realizing such storage typically utilize some type of storage media, such as photorefractive crystals or photopolymer layers, to store 3-D "stacks" of data in the form of pages of data. Typically, coherent light beams from lasers are utilized to perform the addressing, writing and reading of the data from the storage media by directing these beams at a specific region on the surface of the media. Writing is achieved by remembering the interference pattern formed by these beams at this region. Reading is achieved by detecting a reconstructed light beam as it exits the storage medium, the data then being extracted therefrom. Addressing is achieved by the positioning of the laser beams, and this is typically done through the mechanical movement of mirrors or lenses; however, the storage media itself can be moved relative to fixed laser beams.
One application for mass storage devices is that with respect to full-motion video. At present the VCR technology utilizes a magnetic recording on a tape, which tape is then passed over a record/playback head to read the information encoded in the magnetic fields on the tape. One disadvantage to this type of media is that the recording is weakened over time and, in fact, these types of recordings are seldom adequate for long-term archival purposes. With the advent of the CD-ROM digital storage device. Digital storage of video information has become possible. However, most full motion video applications are directed toward movies and these typically require between one to three hours of playback time. The video information required to reproduce a long-playing video in full-motion color is typically in excess of one gigabyte uncompressed. Even when compressed by conventional standards, a full-length, digitally stored feature requires a 12" disk to store all of the information. Through the use of new compression algorithms, it has been possible to compress the data such that a full hour of full-motion color video can be stored on a 51/4" disk, which is a relatively standard disk in the industry. However, this is still inadequate since the disk is not normally removable. Further quality is lost due to the compression algorithm.
Holographic storage devices yield relatively fast access times and allow significantly increased storage over a given area due to the stacking of pages of information within individual storage regions in the media. Further, since the media may be removable, it can act as a container for video movies. However, even with present compression technologies, a large surface area is required. There therefore exists the need to combine the increased storage capacity provided by the holographic storage technology with conventional media tape technology which allows a large amount of information to be contained in a single and portable cartridge.